This invention relates to mechanisms for reading data recorded on magnetic media and for recording data on the media. The invention is more particularly directed to magnetic card reader devices in which a card that has a magnetic stripe is transported past a magnetic pick-up and recording head.
Conventional magnetic card motorized transport systems employ fixed drive mechanisms. These mechanisms typically employ a single drive wheel or capstan and a single opposing idler wheel or roller. With such mechanisms, if a very thin magnetic card is inserted, the card would slip and the head would read out erroneous data. On the other hand, if the card were too thick, there would be a tendency for the card to stick or jam. Unfortunately, magnetic stripe cards tend to vary rather widely in thickness, and a photo-ID laminated magnetic card can vary in thickness from about 0.025 to 0.040 inches. Consequently, these conventional card reader devices have often encountered problems in use.
Another problem with card readers comes about because of the tendency of cards to vary in thickness, or to become warped or curled. If the card has an uneven surface, the magnetic head can come out of contact with the magnetic stripe, causing misreading during pickup or causing writing of errors on recording.
A third problem with the card transport mechanisms of conventional readers is that drive and idler wheels can develop a set or flat spot from remaining depressed against each other during times of non-use. Consequently, there is a tendency for the drive and idler wheels to become somewhat out-of-round at the circumferential surface. This can lead to jamming, or can produce errors in either the pickup or write cycles during transport of the card.
Still another problem of conventional card readers is the problem of "skew", i.e., a tendency of the card to turn in the reader transport mechanism, so that the head and magnetic stripe traverse one another obliquely. If there is a single drive roller, skewing is unavoidable. The data recorded on the card's magnetic stripe occurs as magnetic transitions that are perpendicular to the longitudinal direction of the stripe. If the card becomes skewed, these transitions begin to cross the gaps on the magnetic head out of proper synchronism, and errors are generated. For example, skewing of a magnetic striped card can change a credit value e.g. from $1.00 to $10.00, or to a different code. Severe skewing can totally garble the data and can make encrypted data unreadable by the mechanism.
A previously proposed magnetic card reader which has fixed drive and idler rollers, and a rigidly mounted head is described in U.S. Pat. No. 4,599,510. Another card reader with a stepped-diameter drive roller arrangement to compensate for skew is described in U.S. Pat. No. 3,899,659. Aspects of other magnetic reading/writing devices are described, e.g., in U.S. Pat. Nos. 4,377,828; 4,585,929; 3,890,644; 3,737,884; 3,940,796; and 4,628,386.